Hydrocyanation catalyst systems, particularly pertaining to the hydrocyanation of ethylenically unsaturated compounds, are known in the art. For example, systems useful for the hydrocyanation of 1,3-butadiene (BD) to form pentenenitrile (PN) and in the subsequent hydrocyanation of pentenenitrile to form adiponitrile (ADN) are known in the commercially important nylon synthesis field.
The hydrocyanation of ethylenically unsaturated compounds using transition metal complexes with monodentate phosphite ligands is documented in the prior art. See, for example, U.S. Pat. Nos. 3,496,215; 3,631,191; 3,655,723 and 3,766,237, and Tolman et al., Advances in Catalysis, 1985, 33, 1. The hydrocyanation of activated ethylenically unsaturated compounds, such as with conjugated ethylenically unsaturated compounds (e.g., BD and styrene), and strained ethylenically unsaturated compounds (e.g., norbornene) proceeds without the use of a Lewis acid promoter, while hydrocyanation of unactivated ethylenically unsaturated compounds, such as 1-octene and 3-pentenenitrile (3PN), requires the use of a Lewis acid promoter. Recently, catalyst compositions and processes for the hydrocyanation of monoethylenically unsaturated compounds using zero-valent nickel and bidentate phosphite ligands in the presence of Lewis acid promoters have been described; for example in U.S. Pat. Nos. 5,512,696; 5,723,641 and 6,171,996.
U.S. Pat. No. 3,903,120 describes the preparation of zerovalent nickel complexes of the types Ni(MZ3)4 and Ni(MZ3)2A; wherein M is P, As or Sb; Z is R or OR, wherein R is an alkyl or aryl radical having up to 18 carbon atoms and may be the same or different, and at least one Z is OR; A is a monoolefinic compound having 2 to 20 carbon atoms; the R radicals of a given MZ3 of Ni(MZ3)2A preferably being so chosen that the ligand has a cone angle of at least 130′; are prepared by reacting elemental nickel with the monodentate MZ3 ligand at a temperature in the range of 0° C.-150° C. in the presence of a halogen-containing derivative of the monodentate MZ3 ligand as a catalyst. A more rapid reaction is realized by carrying out the preparation in an organonitrile solvent.
U.S. Pat. No. 4,416,825 also describes an improved, continuous process for the preparation of hydrocyanation catalysts comprising zerovalent nickel complexes with monodentate organophosphorus compounds (ligands) by controlling the temperature of the reaction relative to the amount of monodentate ligand and conducting the reaction in the presence of a chlorine ion and organic nitrile such as adiponitrile.
There are several processes that can be used to make nickel catalyst complexes with phosphorous-containing ligands. One method is a reaction between nickel bis(1,5-cyclooctadiene) [NI(COD)2] and a phosphite ligand; however, this process is not very economical because of the high costs of Ni(COD)2. Another process involves the in situ reduction of anhydrous nickel chloride with zinc dust in the presence of the phosphite ligand. For this reaction to be successful, the nickel metal must react with the phosphorous-containing ligand at a sufficient rate to produce the nickel complex.
U.S. Pat. No. 6,171,996 describes zero-valent nickel complexes comprising bidentate phosphite ligands prepared or generated according to techniques well known in the art, as described, for example, in U.S. Pat. Nos. 3,496,217; 3,631,191; 3,846,461; 3,847,959 and 3,903,120. For example, divalent nickel compounds may be combined with a reducing agent, to serve as a source of zero-valent nickel in the reaction. Suitable divalent nickel compounds are said to include compounds of the formula NiY2 where Y is halide, carboxylate, or acetylacetonate. Suitable reducing agents are said to include metal borohydrides, metal aluminum hydrides, metal alkyls, Zn, Fe, Al, Na, or H2. Elemental nickel, preferably nickel powder, when combined with a halogenated catalyst, as described in U.S. Pat. No. 3,903,120 is also a suitable source of zero-valent nickel.
In comparison to monodentate phosphorus-containing ligands, bidentate phosphorus-containing ligands generally react more slowly with nickel metals described in the above references. One example of a suitable nickel metal is the INCO type 123 nickel metal powder (Chemical Abstract Service registry number 7440-02-0), derived from the decomposition of nickel carbonyl at elevated temperatures.
Many nickel salts can be converted to nickel metal by reduction with hydrogen at elevated temperatures. Potential sources are nickel oxide, nickel formate, nickel oxalate, nickel hydroxide, nickel carbonate, and basic nickel carbonate (BNC). BNC production has been disclosed by R. M. Mallya, et al. in the Journal of the Indian Institute of Science 1961, Vol. 43, pages 44-157 and M. A. Rhamdhani, et al., Metallurgical and Materials Transactions B 2008, Vol. 39B, pages 218-233 and 234-245.